This invention relates to a hydrostatic piston machine.
Heretofore various types of hydrostatic piston machines have been known. For example, one known hydrostatic piston machine has a cylinder block which is rotatable around a pintle and in which peripherally distributed pistons are guided radially in relation to the pintle. Further, the pistons have support surfaces at their outer ends which are guided along plane guiding surfaces of an annular guide member, the guide surfaces being tangential to a circular cylindrical surface whose axis is eccentric of the cylinder block axis. The guide member is in turn, mounted by way of two sidewalls on the pintle about the axis of the circular cylindrical surface. The pintle also has two ports which co-operate with the cylinder block, one port communicating with a bore for a high-pressure hydraulic medium while the other port communicates with a bore for a low-pressure hydraulic medium.
In machines of this kind there are problems for the mountings between the pintle and the cylinder block, and between the pintle and the guide member, particularly if the machine is to be operated in a wide pressure range, e.g. from 100 to 1000 bar, and is also intended for high power outputs, e.g. 1000 HP.
Thus, suitable bearings must be provided to ensure reliable operation. However, the previously known bearings have not been satisfactory. For example, bearings are known which are relieved of load via an oil cushion. Generally, the oil supply to the bearing is unthrottled. In these conditions, the bearing parts contact one another during starting up and during operation, and for this reason the oil must have good lubrication properties. Despite the advantage of low oil losses and low bearing loading in the event of seizure, there are the disadvantages that there is a relatively high bearing friction, the starting characteristic is poor, only oil having good lubricating properties can be used for the bearing, and the maximum possible operating pressure is very limited.
Bearings are also known which have a complete hydrostatic load-relief system. As long as there is a sufficiently high oil pressure, the parts which move in relation to one another do not contact one another. Usually, the oil is supplied to a hydrostatic bearing pocket via a throttle which, together with a bearing gap around the pocket, forms a system which automatically adapts the pressure in the bearing pocket to the bearing load at any time. The friction existing in such bearings during starting up and operation is minimal. It is also possible to use a pressure medium having poor lubricating properties, e.g. silicone oil. However, the disadvantage of such bearings is relatively high oil loss and, in the event of a throttle becoming clogged, the bearing is completely without lubrication and, thus, exposed to the full bearing loading.
Finally, bearings are known which operate with complete hydrostatic relief but without a throttle in the oil supply. In such cases, automatic regulation of the pressure in the bearing pocket is impossible; the magnitude of the bearing gap may be zero or large at any pressure. Such bearings thus have an unstable characteristic and a relatively high oil loss. Further, it is difficult to dimension the bearing pocket because the pressure profile of the pocket cannot be accurately defined. This difficulty applies particularly if the machine is intended for high operating pressures. On the other hand, a bearing of this kind has the advantage of reduced friction and the fact that the bearing loading on seizure is less than with the other two types of bearing mentioned above.
Accordingly, it is an object of the invention to improve the mounting of a cylinder block on a pintle of a hydrostatic piston machine.
It is another object of the invention to improve the mounting of a guide member on a pintle of a hydrostatic piston machine.
It is another object of the invention to provide for a reliable operation of a hydrostatic piston machine over a wide pressure range and with high outputs.
Briefly, the invention is directed to a piston machine comprised of a pintle, a cylinder block which is rotatably mounted on the pintle, a plurality of peripherally distributed pistons slidably mounted in the cylinder block radially relative to the pintle and a guide member about the pistons which has a pair side walls rotatably mounted on the pintle. Each of the pistons is provided with a support surface at an outer end while the guide member is provided with a plurality of plane guide surfaces, each of which has a respective piston support surface guided thereon. In addition, each of the guide surfaces is disposed tangentially of circular cylindrical surface having an axis eccentric to the axis of the pintle.
In addition, a pair of ports are provided in the pintle in facing relation to the cylinder block and a pair of bores are provided in the pintle interior to conduct a high-pressure hydraulic medium and a low-pressure hydraulic medium to and from the respective ports.
In accordance with the invention, the high-pressure bore communicates with one of the ports to deliver or discharge an unthrottled flow of high-pressure hydraulic medium thereto or therefrom respectively while the second bore communicates with the other port to discharge or deliver low-pressure hydraulic medium therefrom or thereto respectively. In addition, a pair of hydrostatic bearing pockets are provided in the pintle facing the cylinder block on opposite sides of the high-pressure port. Each of these bearing pockets connects via a throttle with the high-pressure bore such that a throttled flow of high-pressure medium is delivered by the throttle to the respective pockets.
In addition, a second pair of hydrostatic bearing pockets are provided in the pintle and each of these pockets facing a respective side wall on the opposite side of the pintle from the high-pressure port. Also, a throttle connects each of these pockets to the high-pressure bore conducting a throttled flow of high-pressure medium. Still further, a further pair of bearing pockets are formed in the pintle with each pocket facing a respective side wall on a side opposite the high-pressure port. Further, each of these pockets communicates with the high-pressure bore to receive an unthrottled flow of high-pressure medium therefrom.
With this configuration, at least two hydrostatic bearing pockets are provided at each bearing point, at least one of them having an unthrottled pressure medium supply and at least one having a throttled pressure medium supply. The advantage of this is that the share of the two bearing pockets in the partial relief of the bearing can be adjusted within specific limits, i.e. by altering the cross-sections of the throttles. The throttles cross-sections can be so dimensioned that perfect conditions relative to the bearing clearance apply throughout the range of operation. Generally, the main share of the relief will be assigned to the bearing pockets having the unthrottled pressure medium supply. If one of the throttles breaks down due to clogging, the bearing loading is still relatively small because the bearing pocket with the unthrottled pressure medium supply remains intact. Another advantage is that a pressure medium having poor lubricating properties can be used for the machine.